Apparatus for controlling AC motor

Abstract

In an apparatus, a controller performs, as a calculation of d- and q-axis values of a current vector, a first task and a second task. The first task expands one of a measured first phase current and another phase current into Fourier series of the corresponding phase current as a function of an electric rotational angle of an AC motor. The first task extracts a first-order component from the Fourier series to obtain first and second Fourier coefficients of the first-order component. The second task calculates the d-axis value as a first sum of the first and second Fourier coefficients to which temporally-invariant constants of a first pair have been multiplied, and the q-axis value as a second sum of the first and second Fourier coefficients to which temporally-invariant constants of a second pair have been multiplied.

What is claimed is: 
     
       1. An apparatus for controlling a three-phase AC motor, the apparatus comprising:
 an inverter to which DC power is input, the inverter comprising a plurality of switching elements connected to the AC motor; 
 a current sensor member measuring at least one phase current flowing in the AC motor as a first phase current; and 
 a controller configured to: 
 calculate a d-axis value and a q-axis value of a current vector in a d-q coordinate system defined in the AC motor based on the measured first phase current; 
 perform, based on the calculated d- and q-axis values of the current vector, at least one of a current-feedback task and a torque-feedback task, 
 the current-feedback task: 
 comparing the calculated d-axis value and q-axis value fed back from the AC motor with respective d-axis command current and q-axis command current, 
 performing switching of the plurality of switching elements based on a result of the comparison to convert the DC power to controlled AC power, and 
 applying the controlled AC power to the AC motor, thus driving the AC motor, 
 the torque-feedback task: 
 estimating torque of the AC motor based on the calculated d- and q-axis values of the current vector, 
 comparing the estimated torque fed back from the AC motor with request torque, 
 performing switching of the plurality of switching elements based on a result of the comparison to convert the DC power to controlled AC power, and 
 applying the controlled AC power to the AC motor, thus driving the AC motor, 
 the controller being configured to, as the calculation of the d-axis value and the q-axis value of the current vector, perform a Fourier-coefficient obtaining task and a current-vector calculating task, 
 the Fourier-coefficient obtaining task being configured to:
 expand one of the measured first phase current and another phase current into Fourier series of a corresponding one of the measured first phase current and the another phase current as a function of an electric rotational angle of the AC motor, the another phase current flowing the AC motor and estimated based on the measured first phase current, and 
 extract a first-order component from the Fourier series to thereby obtain first and second Fourier coefficients of the first-order component, 
 
 the current-vector calculating task being configured to:
 multiply the first and second Fourier coefficients by each of a first pair of temporally-invariant constants and a second pair of temporally-invariant constants; and 
 calculate a first sum of the first and second Fourier coefficients, which have been respectively multiplied by the temporally-invariant constants of the first pair, and a second sum of the first and second Fourier coefficients, which have been respectively multiplied by the temporally-invariant constants of the second pair, to thereby obtain the d-axis value and the q-axis value of the current vector. 
 
 
     
     
       2. The apparatus according to  claim 1 , wherein:
 the current sensor member comprises current sensors respectively measuring two-phase currents flowing in the AC motor as the first phase current and a second phase current; 
 the Fourier-coefficient obtaining task is configured to:
 expand the measured first phase current flowing in the AC motor into the Fourier series of the first phase current as a function of the electric rotational angle of the AC motor 
 expand the measured second phase current flowing in the AC motor into second Fourier series of the first phase current as a function of the electric rotational angle of the AC motor; 
 extract the first-order component from the Fourier series of the first phase current to thereby obtain the first and second Fourier coefficients of the first-order component for the first phase current; and 
 extract a second first-order component from the second Fourier series of the second phase current to thereby obtain first and second Fourier coefficients of the first-order component for the second phase current; and 
 
 the controller is configured to: 
 perform the current-vector calculating task using the first and second Fourier coefficients of the first-order component for each of the first and second phase currents, thus calculating: 
 a first d-axis value and a first q-axis value for the first phase current as a first candidate set of the d- and q-axis values of the current vector; and 
 a second d-axis value and a second q-axis value for the third phase current as a second candidate set of the d- and q-axis values of the current vector; and 
 calculate an average of the first d-axis value of the first candidate set and the second d-axis value of the second candidate set to calculate the d-axis value of the current vector, and an average of the first q-axis value of the first candidate set and the second q-axis value of the second candidate set to calculate the q-axis value of the current vector. 
 
     
     
       3. The apparatus according to  claim 1 , wherein:
 the current sensor member comprises current sensors respectively measuring two-phase currents as the first phase current and a second phase current flowing in the AC motor; 
 the controller is configured to estimate, as the another phase current, a remaining third phase current based of the measured first and second phase currents and Kirchhoff's law; 
 the Fourier-coefficient obtaining task is configured to: 
 expand the estimated third phase current flowing the AC motor into the Fourier series of the estimated third phase current as a function of the electric rotational angle of the AC motor, and
 extract the first-order component from the Fourier series to thereby obtain the first and second Fourier coefficients of the first-order component; and 
 
 the controller is configured to perform the current-vector calculating task using the first and second Fourier coefficients of the first-order component for the third phase currents, thus obtaining the d-axis value and the q-axis value of the current vector. 
 
     
     
       4. The apparatus according to  claim 1 , further comprising:
 a current obtaining unit configured to obtain a second phase current flowing in the AC motor based on one of measurement of the second phase current from the AC motor and estimation of the second phase current based on the measured first phase current; 
 a three-phase to two-phase converter configured to convert the first phase current and the second phase current into to a second d-axis value and a second q-axis value of a second current vector; and 
 a selector configured to select one of d- and q-axis values of the current vector obtained by the current-vector calculating task; and the second d- and q-axis values of the second current vector according to at least one of a rotational speed of the AC motor, a request torque for the AC motor, and a modulation factor of the inverter. 
 
     
     
       5. The apparatus according to  claim 1 , wherein:
 the current-vector calculating task is configured to calculate the temporally-invariant constants of each of the first pair and the second pair based on an assumption that coefficients of sine and cosine functions included in a phase-current recalculation equation are equal to coefficients of sine and cosine functions included in a two-phase to three-phase conversion equation, 
 the phase-current recalculation equation calculating the first phase current based on the Fourier-coefficients of the first-order components of the first phase current, 
 the two-phase to three-phase conversion equation converting B- and q-axis currents to three-phase currents flowing in the AC motor. 
 
     
     
       6. The apparatus according to  claim 2 , wherein:
 the current-vector calculating task is configured to calculate the temporally-invariant constants of each of the first pair and the second pair based on an assumption that coefficients of sine and cosine functions included in a phase-current recalculation equation are equal to coefficients of sine and cosine functions included in a two-phase to three-phase conversion equation, 
 the phase-current recalculation equation calculating the first phase current based on the Fourier-coefficients of the first-order components of the first phase current, 
 the two-phase to three-phase conversion equation converting d- and q-axis currents to three-phase currents flowing in the AC motor. 
 
     
     
       7. The apparatus according to  claim 3 , wherein:
 the current-vector calculating task is configured to calculate the temporally-invariant constants of each of the first pair and the second pair based on an assumption that coefficients of sine and cosine functions included in a phase-current recalculation equation are equal to coefficients of sine and cosine functions included in a two-phase to three-phase conversion equation, 
 the phase-current recalculation equation calculating the first phase current based on the Fourier-coefficients of the first-order components of the first phase current, 
 the two-phase to three-phase conversion equation converting B- and q-axis currents to three-phase currents flowing in the AC motor. 
 
     
     
       8. The apparatus according to  claim 4 , wherein:
 the current-vector calculating task is configured to calculate the temporally-invariant constants of each of the first pair and the second pair based on an assumption that coefficients of sine and cosine functions included in a phase-current recalculation equation are equal to coefficients of sine and cosine functions included in a two-phase to three-phase conversion equation, 
 the phase-current recalculation equation calculating the first phase current based on the Fourier-coefficients of the first-order components of the first phase current, 
 the two-phase to three-phase conversion equation converting B- and q-axis currents to three-phase currents flowing in the AC motor. 
 
     
     
       9. An apparatus for controlling a three-phase AC motor, the apparatus comprising:
 an inverter to which DC power is input, the inverter comprising a plurality of switching elements connected to the AC motor; 
 a current sensor member measuring at least one phase current flowing in the AC motor as a first phase current; and 
 a controller configured to: 
 calculate a d-axis value and a q-axis value of a current vector in a d-q coordinate system defined in the AC motor based on the measured first phase current; 
 perform, based on the calculated d- and q-axis values of the current vector, at least one of a current-feedback task and a torque-feedback task, 
 the current-feedback task: 
 comparing the calculated d-axis value and q-axis value fed back from the AC motor with respective d-axis command current and q-axis command current, 
 performing on- and off operations of the plurality of switching elements based on a result of the comparison to convert the DC power to controlled AC power, and 
 applying the controlled AC power to the AC motor, thus driving the AC motor, 
 the torque-feedback task: 
 estimating torque of the AC motor based on the calculated d- and q-axis values of the current vector, 
 comparing the estimated torque fed back from the AC motor with request torque, 
 performing on- and off operations of the plurality of switching elements based on a result of the comparison to convert the DC power to controlled AC power, and 
 applying the controlled AC power to the AC motor, thus driving the AC motor, 
 the controller being configured to, as the calculation of the d-axis value and the q-axis value of the current vector, perform a filtering task and a current-vector calculating task, 
 the filtering task being configured to:
 filter one of the measured first phase current and another phase current to emphasize a first-order component of a corresponding one of the measured first phase current and the another phase current, thus obtaining first and second coefficients of the first-order component, 
 
 the current-vector calculating task being configured to:
 multiply the first and second coefficients by each of a first pair of temporally-invariant constants and a second pair of temporally-invariant constants; and 
 calculate a first sum of the first and second coefficients, which haven been respectively multiplied by the temporally-invariant constants of the first pair, and a second sum of the first and second coefficients, which have been multiplied by the temporally-invariant constants of the second pair, to thereby obtain the d-axis value and the q-axis value of the current vector. 
 
 
     
     
       10. The apparatus according to  claim 9 , wherein:
 the current-vector calculating task is configured to calculate the temporally-invariant constants of each of the first pair and the second pair based on an assumption that coefficients of sine and cosine functions included in a phase-current recalculation equation are equal to coefficients of sine and cosine functions included in a two-phase to three-phase conversion equation, 
 the phase-current recalculation equation calculating the first phase current based on the Fourier-coefficients of the first-order components of the first phase current, 
 
       the two-phase to three-phase conversion equation converting d- and q-axis currents to three-phase currents flowing in the AC motor.